Feet flat on the floor, straighten your back and breathe deeply. Don’t think about the things you have to do; just tune in to how it feels to inhale and exhale.

This is called mindfulness meditation, and learning to quiet the mind and get rid of negative thoughts can reduce stress and improve your health.

While forms of mediation have been in use for more than 2,500 years as part of Buddhism and other practices, over the past decade scientists have increasingly studied mindfulness and confirmed some of its benefits. For example, research suggests that meditation learned during an eight-week training can reduce depression, loneliness, and inflammation, and possibly preserve function in the aging brain.

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A longer, more intensive course — three months — produced results that suggested mediation reduces levels of the stress hormone cortisol, and might even trigger biological changes that help people live longer.

Serious research on meditation has been underway for only a little more than a decade. In 2000, there were 70 studies published in peer-reviewed journals using the terms mindfulness, yoga, or meditation; in 2011 there were 560, said David Vago, an associate psychologist at Brigham and Women’s Hospital and instructor in psychiatry at Harvard Medical School.

While meditation improves well-being and even may reduce illness, Vago said much is still not clear: who benefits and who doesn’t, which types work better, and how much is necessary.

A typical mindfulness class for stress reduction lasts about 26 hours over eight weeks, not including homework and practice.

“Even eight weeks of practice on its own can help us become more familiar with how we perceive and evaluate the world,” Vago said.

The longer people practice meditation the better they become at turning off negative self-talk, said Vago, who presented research data on the subject in early April.

When we let our minds wander, he said, they usually go somewhere gloomy — the extra pounds we want to lose, the fight we regret having, a work deadline. Those negative thoughts add stress and drag us down, contributing to ill health. Redirecting those thoughts and stopping negative self-talk can help people feel better, Vago said.

“Your self-talk is an op-ed piece,” said Saron, leader of the Shamatha Project, which led studies of long-term meditators.

Understanding those opinions will help people feel better. “The great majority of individuals, if they do not have trauma in their background, will find a felt-shift with a sense of self-nourishment and calm and replenishment,” Saron said, “if they spend some time in calm, focused attention following any number of different techniques,” such as meditation.

By middle age, some acquired habits are no longer constructive. Santorelli, of UMass, likes to tell the story about a 40-something patient who was stronger and faster than the 70-year-old he regularly played in handball. But the younger man always lost.

“While he’s capable of hitting the ball harder, running farther, probably having more short-term stamina, he’s not using all of his resources well. He’s relying on a way of approaching that doesn’t work for him,” Santorelli said. “What does this [older] guy do? He has finesse.”

Practicing mindfulness meditation, Santorelli said, can teach people to eliminate habits that are dragging them down and make choices that will allow them to become more physically, emotionally, and mentally flexible.

Mindful eating, another form of mindfulness, has also taught some people to eat less and even helped some realize they don’t like certain foods that they thought they had enjoyed.

“Our taste buds actually get tired rather quickly,” said Jean Kristeller, an emeritus professor of psychology at Indiana State University. “The mindfulness can help people undo habits that have been there for decades.”

Society tends to send the message that certain foods are bad, and that we shouldn’t eat for comfort, but Kristeller disagrees.

“We really emphasize that eating food for a small amount of comfort is normal and natural,” said Kristeller who is scheduled to teach her method at the Kripalu Center for Yoga & Health in Stockbridge in June. “What we find is when people tune into [what they eat] is that they don’t tend to overeat, they do tend to lose weight.”

Another advantage to meditation: It can be started at any age, said Shauna Shapiro, associate professor of counseling psychology at Santa Clara University.

Shapiro said she taught her grandfather to meditate at age 80, when the pain from his arthritis had became unbearable. “I remember one day he said to me, [meditation] hasn’t changed the level of pain I experience, but my relationship to it is completely transformed and my quality of life is so much better. Now I can live my life fully with my pain.’ ”

Stress and pain are part of everyone’s life, Shapiro said. “But when we resist that pain, or the divorce or the traffic or whatever it is, we suffer.”

The goal is not to resign ourselves to these stresses, she said; rather it’s to acknowledge and deal with “this is how things are right now. We accept them not because we like them, but because they already are this way,” Shapiro said.